Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/507

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4. With the affiftance of air, by fermenting, putrifying, agitating, exciting, and adding other parts capable of dil- folving.

5. With fermented fpirits, by diluting, infufing, boiling, di- ftilling, mixing, and making oils thinner.

6. With alkaline falts, by calcining, torrefying, burning, melting, mixing, and feparating, according to the various force of a dry fire employed.

7. By volatile alkaline falts, by fubliming in the dry way, and by diluting, diftilling, and'digefting in the moift way.

8. With fixed alkali falts, aflifted and moved by water and fire, by digefting, boiling, diluting, feparating, and mix- ing.

9. With fixed acid falts, as thofe of alum, fulphur, and vi- triol ; either feparately in a liquid form, or in their calxcs, by diluting, boiling, diftilling, digefting ; or in a dry form, by calcining, roafting, burning, and diftilling.

10. With volatile acid falts, by diluting, digefting, diftilling, and infinuating.

1 r. With compound falts and foaps, by calcining, fublim- ing, diftilling, and digefting, either in a dry or a liquid form.

And 12. with metals, by fufion and amalgamation. This feems an accurate and perfect table of the whole work of folution, and will eafily be underftood in every article, on recollecting the feveral chemical proceiTes. Boerh. Chem. Part. 2. p. 338. See Menstruum, Cycl. and SuppL No phenomenon in nature is more univerfally known, than the /glut ion of falts in common water, but the world has not yet attended to all that might be learned from the obfervati'tns on it.

Mr. Lemery, who examined into this point with great affi- duity, has obferved, 1. That the fir ft effect of water upon a fait, is the reducing it into an inexpreffibly fine powder. a. That it is merely the confequence of this pulverifation carried greatly farther, that every particle of felt whifch, while in larger molecular, fubfided to the bottom of the water, according to the known laws of hydroftatics, be- comes capable of being elevated and fufpended in the water, though in itfelf greatly heavier than that fluid ; that while in a proper ftate of feparation in this manner, they remain imperceptible in all the water, and when by certain acci- dents they again approach one another, they form concreti- ons like their original ones, and again-fubfide in that fluid, in which they floated while in form of this imperceptible powder.

In the foluthns of falts, the fame author obferves, that all the particles of water do not ferve to the fame purpofe ; fome officiating only in the keeping the faline particles fufpended, others in the keeping them afunder, and, as barriers, pre- venting their reunion.

The quantity of water, neceflary to fuftain the particles of all falts in folution, is the fame, but the quantity, required to keep thofe particles from joining again, is different, in regard to every fait. Hence though a quantity of water, equal to the weight of the fait, be fufficient to the fufpenfi- on of its particles, yet every fait requires its own appropri- ated quantity of water to keep it in a ftate of folution ; that is, to keep its particles from cohering together again. In fuch falts, the particles of which are not fubject to form hard concretions, fuch as the fixed fait of tartar, and the like, there requires no more water for a folution than is ne- ceflary to fufpend the particles of the fait ; but in thofe which readily form folid concretions, fuch as common fait, nitre, borax, and the reft, there requires a large quantity befide to act. as a barrier.

The more the particles of any fait are difpofed to reunite, the more water they require to keep them in a ftate of fo- lution ; and hence follows a very remarkable phenomenon, which is the folution of feveral falts fucceffively in the fame water: this is known to be poflible, and the reafon of the whole is this, that when a given fait, requiring a large quantity of water for its folution, is diflolved in that water ; the greater part of that water, which in this folution ferves only to the fecond purpofe of keeping the particles of the fait afunder, is ftill at full liberty to act as water upon an- other fait that fhall be thrown into it. This, however, can be only the cafe in regard to falts which do not naturally ferment with one another, becaufe the whole procefs is difturbed by fuch a fermentation, and, in confequence of it, there is a third fait formed, which is not the fame with either ot the two; and the confequence of the formation of this fait, is the precipitation of the me- tallic, or earthy matter, which was the bale of one of the other falts. Thus an alkaline fait, added to a folution of alum, or faccharum faturni, takes up the acid of either of thefe falts, and becomes, by its mixture with that acid, a new concrete fait, and at the fame time throws down, in precipitation, the terreftrial bafe of the alum, and the me- tailiconc of the fait of lead.

To return to thofe falts which excite no fermentation with one another. In regard to thefe, when a quantity of water has diflolved as much as it can retain of one, it will rea- -dily take in and difTolve a fecond ; and the particles of this Suppl. Vol- II.

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not fermenting with thofe of the fait firft diiTolved, will re^ main fufpended, and the Water which diffolves them, .and which in the firft folution ferved'only. as an: intermedium to keep the particles of that fait afunder, ferve as well to that purpofe, now they are impregnated with this new fait* as they' did before.

The reafon hitherto given for this phenomenon was* that the particles of different falts, though fufpended in fuch manner in the fame fluid, that they were every moment coming into contact with one another, yet had no tendency from nature to cohere, or precipitate one another; but that whenever, by futuie accidents, they ihould be brought to concrete, they would do it feparately, each in its own pure ftate; but this reafon, though true, is an imperfect one. In thefe fucceflive folutiom of falts in the fame water, the fecond fait produces, a remarkable effect, which no body, till Mr. Lemery, feems to have taken notice of; which, is, that while this is diiTolved in a liquor, which :bt.fore ferved as an intermedium to keep the particles of another fait afunder, it encreafes by its whole quantity the quantity of that' intermedium, and becomes itfelf a fort of intermedium to the .particles of the firft diflolved fait ;' and by this means die liquor, which had before diflolved as much as it could contain of the firft fait, now becomes able to take up fame more of it, and will, in reality, perfectly diiTolve an addi- tional quantity : this was an experiment well known, but never underftood before.

It is well known that fait of tartar does not ferment with fait petre, nor does it take any thing from this fait, or at all alter by being mixed with it, which is quite different from .the effect on mixing it, as before obferved, with alum, or faccharum faturni ; on this principle, and on the known property of fait of tartar bei-tg diffolved in a fmaller quantity of water than any other fait ; or, in other words, of water's diflblving more fait of tartar than of any other fait, Air. Lemery refolved on the trial, whether water, which had already diflolved as much nitre as it could contain* would not, on the addition of fait of tartar, diflblve a larger quantity of frefh nitre, than on the addition of fal armo- niac, or any ether fait: but what appeared very ftrange was, that after two days (landing of a folution of nitre, with about a fourth part of the quantity of fait of tartar added, there was found a white powder at the bottom. The liquor being examined on this, was found to be a lixivium of fait pf tartar, and the powder at the bottom, fait petre^ On adding frefh quantities of fait of tartar, new precipi- tations were afterwards formed, and, in fine, all the fait petre which had been diffolved was feparated. The fait petre being examined, by all trials proved true fait petre, as pure and unmixed as when put in ; and the liquor being evaporated, the fait of tartar was found equally pure. Salt of tartar tried afterwards in the fame manner with folutions of other falts* with which it does not raife any fermentation, was found to have the fame effect, precipitating all equally out of the folution.

In the common precipitations of falts* fucli as alum and fugar of lead, by means of an alkali, the alkali feizes upon the acid of thofe falts, and by that means effects the thing, and therefore itfelf becomes changed into another fait, and the precipitate, robbed of that acid, is no longer thcfalt it was, but merely its bafe : but here the falts, both alkali and neutral, remain the fame thzy were before, both pure and unmixed, and the whole procefs feems only one of them taking the place of the other.

The falts which are capable of fuccefnve fehttions in the fame water, and of remaining fufpended together in it, muft he all of the neutral kind 5 that is, they muft be felts eompofed of acids, engaged in fuch manner in the pores of thir bafes, as to fill the whole* and leave no void fpaces for the pene- tration of other acids- But this is by no means the cafe" with fait of tartar, which being wholly fpunge-like in its ftructure* readily admits all forts of acids* and ferments with them ; and therefore is very capable of divefting other falts of that, on the prefence of which their natural ftate, as fdts of a particular kind, depends.

Every alkali fait is, as it were, an efl'ential fait, in part de- compounded ; that is, it is the earth;: part of fuch fait, the acid'parts of which have been driven off by fire, and when there is only fo much left, as may give the whole a faline form ; for if all the acids were to be driven off, the re- mainder would not be an alkali, nor yet a fait, but a mere Ample earth ; as is the cafe in the caput mortuum of fpirit of nitre diftilled by a retort, the rehduum from this diftilla- tion being a mcre'dead earth, indilToiubie in water, and al- together different from the fixed alkali produced by burning the fame nitre with charcoal. What proves, alfo, that thefe alkalis are only the matrix of the compound falts diverted of their acids, is, that if fpirit of nitre be pcuicd upon the alkali fait of nitre made with charcoal, true nitre is regene- rated. Mem. Acad. Par. 1724.

When folutions of falts are congealed, the ice often afford;- very pretty figures ; but it is to be obferved, that the fame fait does not always give the fame figures. Thus the fame folution of vcrdijreafe, frozen by means of fnow and jWr, 2 T 1 1 aftard*